***********************************************************
** At least one step is needed to run an CalculiX analysis of FreeCAD
** written by write_step_begin function
*STEP
*FREQUENCY, SOLVER=MATRIXSTORAGE
1,0.0,100000.0

I include SOLVER=MATRIXSTORAGE option for obtaining the mass and stiffness matrices (.mas) and (.sti) files as described in the calculix manual

***********************************************************
** At least one step is needed to run an CalculiX analysis of FreeCAD
** written by write_step_begin function
*STEP
*FREQUENCY, MATRIXSTORAGE
1,0.0,100000.0

***********************************************************
** At least one step is needed to run an CalculiX analysis of FreeCAD
** written by write_step_begin function
*STEP
*FREQUENCY, MATRIXSTORAGE
1,0.0,100000.0